This invention concerns so called automatic antiskid devices of the kind that, for instance, is described in U.S. Pat. No. 4,299,310. Anti-skid devices of this kind include a pulley on which has been arranged a number of chains. In use, the pulley is brought in contact with the side of a vehicle wheel, causing the pulley to rotate with the wheel, and the chain pieces are thrown in under the wheel, thereby improving the traction of the vehicle wheel. The chain-provided pulley is journaled in the outer end of an arm actuated by, for instance, a pressurized air-cylinder so that the pulley can be moved from its working position in contact with the side of the vehicle wheel and a parking postion out of the way. This construction has turned out very well in practice even if other and new constructions have been added to the market.
In order to secure that the chain-provided pulley always is brought in contact with the vehicle wheel at the correct position, the amount of play that is acceptable in the journaling of the arm at its inner pivot point is limited. Furthermore, the arm must be very easily pivotable in order not to increase size and cost of the pressurized aircylinder. On the other hand, the journaling of the pivotpoint may not became too expensive. Due to the limited amount of space in many vehicles today, the journaling of the the arm cannot be bulky.
In order to handle the very great loads that the arm is subjected to, the arm has been journaled in ball bearings. This works very well to start with. However, the ball bearings wear out prematurely. The exchange frequency has turned out to be substantially independent of the quality of the bearings. An increased play in the bearings results in a poorer function and possible damage to other parts of the antiskid device. The journaling of the arm has thus turned out to be a weak point, and a better bearing is needed.